1. Field of the Invention
The present invention concerns methods and devices for the determination of the position of a local coil for a magnetic resonance apparatus.
2. Description of the Prior Art
Magnetic resonance apparatuses for examination of patients, in particular by means of magnetic resonance tomography are known from DE 10 342 15B4, for example.
Modern magnetic resonance systems normally operate with multiple different antennas (also called coils in the following) to emit radio-frequency pulses for nuclear magnetic resonance excitation and/or to receive the induced magnetic resonance signals. A magnetic resonance system typically has a larger coil that is normally permanently installed in the apparatus, known as a whole-body coil (also called a body coil or BC), as well multiple small local coils (also called surface coils or LCs). In contrast to the whole-body coil, the local coils serve to acquire detailed images of body parts or organs of a patient that are located relatively near to the body surface. For this purpose the local coils are applied directly at the point of the patient at which the region to be examined is located. Given a use of such a local coil, in many cases the transmission occurs with the whole-body coil (as transmission coil) permanently installed in the magnetic resonance system and the induced magnetic resonance signals are received with the local coil (as reception coil).
The position of local coils used to receive the MR signals in the medical MR imaging can vary relative to the patient table and to the patient. Optical detection with a camera and RFID methods has been considered as solution approaches to determine the position. An additional known method uses the MR imaging itself in order to localize the coils. Disadvantages of the optical detection and the RFID method are the necessary additional components in the coil and/or in the MR scanner that incur costs. Disadvantages of the MR imaging are the time cost (a separate measurement is required for every bed (patient) position) and the problematic reliability (dependency on MR imaging parameters, for example B0 homogeneity, B1 homogeneity, in particular at the edge of the imaging volume).